The present invention relates to a composite photocatalyst for the photochemical degradation of refractory waste materials and to a method of using the photocatalyst for treating refractory waste materials which are known to withstand high temperature oxidation, such as chlorinated aromatic compounds and metal cyanide complexes, to degrade same. The invention is particularly directed to the detoxification of PCB's (polychlorinated biphenyls).
Previous reports have described the dechlorination of PCB's involving a photocatalytic process using titanium dioxide. The scope of the potential for photocatalysis in waste treatment was reported in a paper by Carey and Oliver, Water Poll. Res. J. of Canada, Vol. 15, No. 2, 1980, pp. 157-185. In this report, the authors were able to demonstrate laboratory potential for all of the following reactions using titanium dioxide:
1.Oxidation of cyanide. PA1 2. Decoloration of pulp mill black liquors. PA1 3.Dechlorination of chlorobezoate to benzoate. PA1 4.Increase of biodegradability of a lignin model. PA1 5.Detoxification of AROCLOR 1254 (trademark; a polychlorinated biphenyl).
Titanium dioxide has been the most popular of metal oxide semiconductors for study of photocatalysis for nearly 50 years. It has a band gap of 3.2 eV and absorbes light starting from 350 nm and continuing toward higher energy. Consequently, there has been continuing interest in methods for the sensitization of titanium dioxide to allow use of longer wavelength.
Japanese Patent Publication No. 57-166,175, for example, describes the use of titanium dioxide with 5% platinum deposited thereon as a photocatalyst for decomposing PCB's under visible and ultraviolet light. Such a photocatalyst, however, is effective for all practical purposes on PCB in water only, and not on PCB in oil, the more normally encountered form of PCB waste.